The present invention is directed to a head suspension assembly having a torsion spring in a spring region and a hinge structure held in positive engagement by a tether.
Information storage devices typically include a head for reading and/or writing data onto a storage medium such as a magnetic disk within a rigid disk drive. An actuator mechanism is used to position the head at specific lateral locations or tracks on the magnetic disk. Both linear and rotary type actuators are well known in the art. Between the actuator and the head, a head suspension is required to support the head in proper orientation relative to the disk surface.
The head suspension carries the read/write head so that the head can xe2x80x9cflyxe2x80x9d over the surface of the rigid disk while the disk is spinning. The head is typically located on a head slider having an aerodynamic design so that the head slider flies on an air bearing generated by the spinning disk. The combination of the head slider and the head suspension is referred to as a head suspension assembly. The head suspension includes a load beam having a radius or spring section and a rigid section. A spring or gimballing connection is typically included between the head slider and the rigid section of the load beam so that the head slider can move in the pitch and roll directions of the head to accommodate fluctuations of the disk surface. Such a spring connection can be provided by a gimbal that can be either a separate component connected to the rigid region of the load beam or integrally manufactured at the end of the load beam.
Typically, the spring section of the load beam includes a formed bend or radius. This radius provides the spring or load force and thus a desired load to the head slider for a predetermined offset height, the offset height being a measurement of the distance between the mounting height of the head suspension to the actuator and the head slider at xe2x80x9cflyxe2x80x9d height.
The spring force provided by the spring region obeys a simple Hooke""s law relation. That is, the load force the spring region exerts on the head slider toward the disk is directly proportional to the distance the head slider has been deflected away from the disk by the force created by the air bearing; the greater the deflection, the greater the opposing force, and the less the deflection, the lower the opposing force. The constant of proportionality between the distance the head slider has been deflected and the load force is the spring constant of the load beam.
As this discussion makes clear, the fly height of the head slider above the disk is a balance of the lifting force and the opposing load force. Thus, the load force is one factor that directly determines the height at which the head moves over the disk. This height is critical to high speed, accurate storage and retrieval of data. Further, the industry is constantly pushing the upper limit of the density of information that can be stored on disk drives. The density of information which a head can write to or read from a disk is proportional to the height of the head over the disk. Thus, it is desirable to control the fly height of the head over the disk as precisely as possible while preventing contact between the head and the disk.
However, disk drive manufacturing processes can make fly height control difficult to realize. Handling of the head suspension after production may change the bend or radius thereby altering load force characteristics causing xe2x80x9cload loss.xe2x80x9d
Because of the direct relation between load force and fly height, load loss or spacing variations can impact fly height. One way to minimize the problem is to effectively make the spring region of the load beam more pliable. As noted above, the constant of proportionality between the deflection of the head slider and the opposing load force exerted by the spring region of the load beam is the load beam+s spring constant. It follows that the lower this spring constant, the less effect a change in deflection will have on load force. Thus, lowering the spring constant of the spring region of the load beam acts to minimize the effects of load loss or spacing variation on fly height.
The prior art reveals various methods of lowering the load beam spring constant, such as disclosed in U.S. Pat. No. 5,734,525 (Girard). One method is to elongate the spring region, another is to thin the material from which the spring region is manufactured. A third way is to reduce the thickness of a narrow strip of the spring region thereby effectively creating a hinge about which the load beam may rotate in a direction normal to the load beam.
However, these methods of reducing the load beam spring rate often have other consequences. In addition to providing the aforementioned spring force, the load beam must also provide the rigid link between the disk drive actuator and the head slider/head assembly for precisely positioning the head relative to data tracks on the disk surface. Lowering the spring rate of the load beam using one of the methods enumerated above can affect the load beam""s ability to provide such a rigid link.
Specifically, lowering spring rate as above can increase the head suspension""s vulnerability to high vibration frequencies, which can cause off-track error. This effect is particularly acute at resonance frequencies of the suspension assembly. Thus, it is important to design a suspension assembly so that either its resonance frequencies are higher than the frequencies experienced in the drive environment or the gain (movement of the suspension assembly at the head slider) at resonance frequencies is minimized.
Of most concern in the design of suspension assemblies are the resonance frequencies of the torsional modes and lateral bending (or sway) modes. These modes can result in lateral movement of the head slider at the end of the head suspension assembly and are dependent on cross-sectional properties along the length of the load beam. Torsional modes sometimes produce a mode shape in which the tip of the resonating suspension assembly moves in a circular fashion. However, since the head slider is maintained in a direction perpendicular to the plane of the disk surface by the stiffness of the applied spring force acting against the air bearing, only lateral motion of the rotation is seen at the head slider. The sway mode is primarily lateral motion.
Typically, there are two torsional mode resonant frequencies, which occur below the first sway mode resonant frequency. Various techniques well known in the art are used to design head suspensions so that these first two torsion modes have a minimal effect on read/write performance.
The resonance frequency of the sway mode is normally designed to be higher than the frequencies that are experienced by the load beams in the disk drives within which they are used. However, the techniques described above which can be used to lower load beam spring rate can also reduce the lateral stiffness of the load beam. This has the effect of lowering the sway mode resonant frequency, in some cases to a point below the second torsional mode resonant frequency. If sway gain is high and if a sway resonant frequency is within frequencies that may be experienced in the disk drive, off track error could occur.
The present invention is directed to a head suspension assembly with a hinge structure that de-couples frequency response from the spring rate. The hinge structure also minimizes the change in beam profile relative to z-height. A torsional spring provides a low gram and low spring rate without sacrificing frequency response.
The head suspension has a load beam with a mounting region at a proximal end, a rigid region at a distal end and a tether connecting the mounting region and the rigid region. A hinge structure is located between the rigid region and the mounting region. The hinge structure comprises an interface with first pivot surfaces on the mounting region positively engaged with second pivot surfaces on the rigid region by the tether. A torsional spring is located between the rigid region and the mounting region. The mounting region, rigid region and tether can be a single, continuous piece of material or separate components.
The torsional spring can have a nested configuration, a linear configuration or a serpentine configuration. The hinge structure preferably includes an axis of rotation adjacent to the torsional spring. In one embodiment, the axis of rotation extends through the operating region of the torsional spring. The torsional spring supplies gram load and distributes the stress of loading caused by offset heights generally around the pivot axis of the hinge structure. The stresses are preferably distributed over the entire length of the torsional spring. The tether does not appreciably effect gram load, but rather acts substantially independent of the torsional spring.
The tether can be a separate component or part of the material comprising the mounting region and/or rigid region. One or more bends can be formed in the tether to shorten its effective length and to generate a biasing force between the first and second pivot surfaces. In one embodiment, the tether comprises a member mechanically coupling the mounting region to the rigid region. The tether and the torsional spring can be separate components or can be formed from the same piece of material.
The hinge structure typically comprises a pair of upper tabs and a pair of lower tabs on the mounting region. Alternatively, the upper and lower tabs can be located in the rigid region. In another embodiment, the hinge structure comprises a notch in rails on the rigid region. In another hinge structure, the first pivot surface comprises a horizontal edge on the mounting region and the second pivot surface comprises a vertical edge with a notch on the rigid region.
The present invention can be incorporated into many different types of suspension styles, while still maintaining the pivot axis close to the axis of the torsional spring, including thin beam suspensions, thick beam suspensions, laminate suspensions, hybrid suspensions.
In thin beam suspensions, the hinge structure can be integral with the thin beam or can be a separate piece. Thin beam suspensions are typically constructed from material having a thickness of about 0.0025 inches or less. In thick beam head suspensions, the hinge structure can either be a separate piece or integral with the load beam.
In hybrid head suspensions, both thin and thick beam materials may be used. The hinge structure in a hybrid head suspension can be made from the head suspension material with a stiffener added or can be a separate component. The hinge structure can also be part of the base plate. In laminate head suspensions, the hinge structure can be made from one of the skins of the laminated structure. In another laminate embodiment, a living hinge with an integral torsional spring is provided in a multi-piece head suspension assembly. Various aspects of the torsional spring and/or hinge structure can optionally be part of the base plate.